This invention relates generally to gas turbine engines and, more particularly, to methods and apparatus for regulating fluid flows within a gas turbine engine.
At least some known aircraft gas turbine engines include a fan, a compressor, a combustor, a high pressure turbine, a low pressure turbine, and an augmentor or “afterburner”. Airflow entering the fan is compressed. Airflow exiting the fan is split such that a portion of the flow is directed into the compressor and the remaining portion of the flow, referred to as fan bypass flow, is directed into a bypass passage where it bypasses the compressor, the combustor, the high pressure turbine, and the low pressure turbine. Airflow entering the compressor is compressed and directed to the combustor where it is mixed with fuel and ignited, producing hot combustion gases used to drive both the high pressure and the low pressure turbines. Moreover, at least some known gas turbine engines combine a portion of the fan bypass flow with the airflow exiting the low pressure turbine.
To regulate an amount of bypass air supplied to the augmentor, at least some gas turbine engines include a valve assembly. More specifically, in some known gas turbine engines, the flow of the fan bypass air is regulated based on specific exhaust liner pressure ratio requirements demanded for the type of flight mode of the aircraft.
However, at least some known valve assemblies include a plurality of blocker doors that are adjusted independently to maintain exhaust liner pressure ratio requirements. As such, each blocker door includes a separate kinematics system, which may each include, for example, a plurality of crank-arm shafts and actuators. Accordingly, such valve assemblies are generally relatively complex designs and add additional cost and additional weight to the aircraft.
Furthermore, in at least some known valve assemblies, an aerodynamic throat, with a significantly smaller area than the physical throat, could undesirably form downstream from the physical throat in the outer bypass duct. Such an aerodynamic throat may have unsteady behavior that is difficult to predict and to control. In addition, a valve assembly is a pressure loss device, and, if a downstream aerodynamic throat occurs, there may exist more than one valve position that has the same pressure loss. Some known control systems have difficulty accounting for multiple solutions, such as multiple valve position having the same pressure loss. Unexpected multiple solutions may lead to a control systems failure.